I can not manually enable Avast and when I try to do that, I get an error code:
0x80046401

Avast also reports that C:\Windows\System32\mmc.exe is shutting down the real time shields of Avast. However, a VirusTotal scan of the file doesn't say it is infected (0/47 scanners). The process that avast reports is trying to shut it down keeps changing as you see here:

Moreover, the Service Manager says that the avast service, AvastSvc.exe has been started.

The GUI module of Avast reports that I haven't yet registered Avast but when I check
Maintenance -> Registration, the expiry date is shown to be 7/2/2014.

I also can not generate support packages (zip files with program logs, minidumps, other technical info). When I do, I get another error code: 0x3e3

Have you tried the usual things like uninstalling and then installing it again to see if the problems disappear?
–
user2064000Jul 23 '13 at 17:32

No, I haven't tried that yet. I'll do that and see how it goes. I'm not sure if it'll help though. I might be wrong, but I think the symptoms match that of a rootkit intrusion.
–
VinayakJul 23 '13 at 17:44

Have you contacted Avast for support to determine what the error code means exactly?
–
RamhoundJul 23 '13 at 17:45

I did contact Avast support. I'm waiting on an answer from them. However, a quick Google search revealed this post: forum.avast.com/index.php?topic=129313.0 An Avast expert says it's a Windows error code, but I still don't know what it means.
–
VinayakJul 23 '13 at 17:48

1

I suggest you use a system restore point to before this problem surfaced.
–
RamhoundJul 23 '13 at 18:00